scholarly journals Uroporphyrin accumulation produced by halogenated biphenyls in chick-embryo hepatocytes. Reversal of the accumulation by piperonyl butoxide

1986 ◽  
Vol 237 (1) ◽  
pp. 63-71 ◽  
Author(s):  
P R Sinclair ◽  
W J Bement ◽  
H L Bonkovsky ◽  
R W Lambrecht ◽  
J E Frezza ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Chick Embryo ◽  
De Novo ◽  
Covalent Binding ◽  
Piperonyl Butoxide ◽  
Uroporphyrinogen Decarboxylase ◽  
Drug Induced ◽  
Cytochrome P 450 ◽  
Inhibition Of Metabolism ◽  
Methylenedioxyphenyl Compounds

Cultures of chick-embryo hepatocytes were used to study the mechanism by which 3,4,3′,4′-tetrachlorobiphenyl and 2,4,5,3′,4′-pentabromobiphenyl cause accumulation of uroporphyrin. In a previous paper, an isoenzyme of cytochrome P-450 induced by 3-methylcholanthrene had been implicated in this process [Sinclair, Bement, Bonkovsky & Sinclair (1984) Biochem. J. 222, 737-748]. Cells treated with 3,4,3′,4′-tetrachlorobiphenyl and 5-aminolaevulinate accumulated uroporphyrin and heptacarboxyporphyrin, whereas similarly treated cells accumulated protoporphyrin immediately after piperonyl butoxide was added. Piperonyl butoxide also restored haem synthesis as detected by incorporation of radioactive 5-aminolaevulinate into haem, and decrease in drug-induced 5-aminolaevulinate synthase activity. The restoration of synthesis of protoporphyrin and haem by piperonyl butoxide was not affected by addition of cycloheximide, indicating recovery was probably not due to protein synthesis de novo. Piperonyl butoxide also reversed uroporphyrin accumulation caused by 3,4,5,3′,4′,5′-hexachlorobiphenyl, mixtures of other halogenated biphenyls, lindane, parathion, nifedipine and verapamil. The effect of piperonyl butoxide was probably not due to inhibition of metabolism of these compounds, since the hexachlorobiphenyl was scarcely metabolized. Other methylenedioxyphenyl compounds, as well as ellipticine and acetylaminofluorene, also reversed the uroporphyrin accumulation caused by 3,4,3′,4′-tetrachlorobiphenyl. SKF-525A (2-dimethylaminoethyl-2,2-diphenyl valerate) did not reverse the uroporphyrin accumulation caused by the halogenated biphenyls, but did reverse that caused by phenobarbital and propylisopropylacetamide. We conclude that the mechanism of the uroporphyrin accumulation cannot be due to covalent binding of activated metabolites of halogenated compounds to uroporphyrinogen decarboxylase.

scholarly journals Inhibition of uroporphyrinogen decarboxylase by halogenated biphenyls in chick hepatocyte cultures. Essential role for induction of cytochrome P-448

1984 ◽  
Vol 222 (3) ◽  
pp. 737-748 ◽  
Author(s):  
P R Sinclair ◽  
W J Bement ◽  
H L Bonkovsky ◽  
J F Sinclair
Keyword(s):  
Chick Embryo ◽  
Dose Response ◽  
Essential Role ◽  
Piperonyl Butoxide ◽  
Polycyclic Hydrocarbon ◽  
Decarboxylase Activity ◽  
Uroporphyrinogen Decarboxylase ◽  
Maximal Induction ◽  
Time Required ◽  
Cytochrome P 450

Uroporphyrinogen decarboxylase (EC 4.1.1.37) activity was assayed in cultures of chick-embryo hepatocytes by the changes in composition of porphyrins accumulated after addition of excess 5-aminolaevulinate. Control cells accumulated mainly protoporphyrin, whereas cells treated with 3,4,3′,4′-tetrachlorobiphenyl or 2,4,5,3′,4′-pentabromobiphenyl accumulated mainly uroporphyrin, indicating decreased activity of the decarboxylase. 3-Methylcholanthrene and other polycyclic-hydrocarbon inducers of the P-448 isoenzyme of cytochrome P-450, did not affect the decarboxylase in the absence of the biphenyls. Induction of P-448 was detected as an increase in ethoxyresorufin de-ethylase activity. Pretreatment of cells with methylcholanthrene decreased the time required for the halogenated biphenyls to inhibit the decarboxylase. The dose response of methylcholanthrene showed that less than 40% of the maximal induction of cytochrome P-448 was needed to produce the maximum biphenyl-mediated inhibition of the decarboxylase. In contrast, induction of the cytochrome P-450 isoenzyme by propylisopropylacetamide had no effect on the biphenyl-mediated decrease in decarboxylase activity. Use of inhibitors of the P-450 and P-448 isoenzymes (SKF-525A, piperonyl butoxide and ellipticine) supported the concept that only the P-448 isoenzyme is involved in the inhibition of the decarboxylase by the halogenated biphenyls. The effect of preinduction with methylcholanthrene to enhance inhibition of the decarboxylase was also shown by the increased rate at which porphyrin accumulated from endogenously synthesized 5-aminolaevulinate after treatment of cells with the combination of propylisopropylacetamide and the biphenyls. Antioxidants, chelators of iron, and chromate affected the decrease in decarboxylase activity only if they prevented the induced increase in cytochrome P-448. We conclude that the P-448 and not the P-450 isoenzyme of cytochrome P-450 plays an obligatory role in the inhibition of uroporphyrinogen decarboxylase caused by halogenated biphenyls.

Porphyrinogenic effects in chick embryo liver cell culture of chloramphenicol analogues that are mechanism-based inactivators of cytochrome P-450

1991 ◽  
Vol 69 (4) ◽  
pp. 526-530 ◽  
Author(s):  
R. P. Green-Thompson ◽  
D. S. Riddick ◽  
J. E. Mackie ◽  
G. S. Marks ◽  
J. R. Halpert
Keyword(s):  
Cell Culture ◽  
Chick Embryo ◽  
Rat Liver ◽  
Liver Cell ◽  
Prosthetic Group ◽  
Uroporphyrinogen Decarboxylase ◽  
Compound A ◽  
Liver Cell Culture ◽  
Embryo Liver ◽  
Cytochrome P 450

Structural analogues of chloramphenicol (CAP) cause mechanism-based inactivation of rat liver cytochrome P-450 (P450) either via protein acylation or destruction of the heme prosthetic group. The goal of the present work was to determine whether CAP analogues that cause loss of the P450 heme moiety also cause porphyrin accumulation in chick embryo liver cell culture. The porphyrin profiles produced by exposure of cells to CAP analogues (160 μM) were determined by high-performance liquid chromatography with fluorescence detection. Of three CAP analogues that do not cause loss of the heme moiety of rat liver P450IIB1, two dichloroacetamides were not porphyrinogenic. The third compound, a chlorofluoroacetamide, caused porphyrin accumulation. This result may be due to the presence of P450 isozymes in chick embryo hepatocytes, distinct from rat liver P450IIB1, that are susceptible to destruction by this analogue. Of four CAP analogues that inactivate rat liver P450IIB1 with concomitant heme loss, a dichloroacetamide and two chlorofluoroacetamides caused porphyrin accumulation. The remaining compound, a monochloroacetamide, was not porphyrinogenic, perhaps because the P450 apoprotein cannot be reconstituted with fresh heme drawn from the regulatory "free heme pool" following inactivation by this analogue. Alternatively, there may be no P450 isozyme in chick embryo liver cell culture that is susceptible to inactivation by this compound.Key words: cytochrome P-450, chloramphenicol, chick embryo hepatocyte, mechanism-based inactivation, uroporphyrinogen decarboxylase.

Inhibition of chick embryo hepatic uroporphyrinogen decarboxylase by components of xenobiotic-treated chick embryo hepatocytes in culture

1989 ◽  
Vol 67 (3) ◽  
pp. 246-249 ◽  
Author(s):  
C. A. James ◽  
G. S. Marks
Keyword(s):  
Chick Embryo ◽  
Protein Concentration ◽  
Enzyme Assay ◽  
Uroporphyrinogen Decarboxylase ◽  
Optimum Ph ◽  
Embryo Liver ◽  
Liver Homogenates ◽  
Previous Demonstration ◽  
Sodium Phenobarbital ◽  
Cytochrome P 450

Uroporphyrinogen decarboxylase (UROG-D) activity in the 10 000 g supernatant of 17-day-old chick embryo liver homogenates was determined by measuring the conversion of pentacarboxylporphyrinogen I to coproporphyrinogen I. The optimum pH of the enzyme was found to be approximately 6.0 and enzyme activity was found to be linear with protein concentrations ranging from 0.3 to 2.0 mg/mL. At a protein concentration of 1.2 mg/mL and pH 6.0, the activity was found to be linear for a reaction time of 50 min and to be approximately 10 pmol/(mg protein∙min). This enzyme assay was used to demonstrate that a UROG-D inhibitor, previously reported to accumulate in rodent liver, also accumulates in 3,3′4,4′-tretrachlorobiphenyl (TCBP) and sodium phenobarbital (PB) treated chick embryo hepatocytes in culture. This result accords with the previous demonstration of a TCBP- and PB-induced decrease in UROG-D activity in this system. Uroporphyrin accumulation in chick embryo hepatocyte culture is interpreted as resulting from a combination of two mechanisms, viz., inhibition of UROG-D activity and uroporphyrinogen oxidation to uroporphyrin catalyzed by a cytochrome P-450 isozyme.Key words: uroporphyrinogen decarboxylase, enzyme inhibition, chick embryo hepatocytes, tetrachlorobiphenyl, porphyria.

scholarly journals Inhibition of uroporphyrinogen decarboxylase activity. The role of cytochrome P-450-mediated uroporphyrinogen oxidation

1990 ◽  
Vol 269 (2) ◽  
pp. 437-441 ◽  
Author(s):  
R W Lambrecht ◽  
J M Jacobs ◽  
P R Sinclair ◽  
J F Sinclair
Keyword(s):  
Chick Embryo ◽  
Fold Increase ◽  
Treated Mouse ◽  
Decarboxylase Activity ◽  
Chick Embryos ◽  
Uroporphyrinogen Decarboxylase ◽  
Chemically Induced ◽  
Cytochrome P 450 ◽  
Generating System

It was previously shown that uroporphyrinogen oxidation is catalysed by a form of cytochrome P-450 induced by 3-methylcholanthrene [Sinclair, Lambrecht & Sinclair (1987) Biochem. Biophys. Res. Commun. 146, 1324-1329]. We have now measured uroporphyrinogen oxidation and uroporphyrinogen decarboxylation simultaneously in 10,000 g supernatants from the livers of methylcholanthrene-treated mice and chick embryos incubated with an NADPH-generating system. We found that uroporphyrinogen oxidation is associated with inhibition of uroporphyrinogen decarboxylase activity. The decreased uroporphyrinogen decarboxylase activity was not due to depletion of substrate, since decarboxylase activity was not increased by a 2.6-fold increase in uroporphyrinogen. Uroporphyrinogen oxidation and the associated inhibition of decarboxylase activity were also observed with liver supernatant from methylcholanthrene-treated chick embryo; both actions required the addition of 3,3′,4,4′-tetrachlorobiphenyl. Uroporphyrinogen oxidation catalysed by microsomes from a methylcholanthrene-treated mouse inhibited the uroporphyrinogen decarboxylase activity in the 100,000 g supernatant. Ketoconazole, an inhibitor of cytochrome P-450, prevented both uroporphyrinogen oxidation and the inhibition of uroporphyrinogen decarboxylation. The addition of ketoconazole to mouse supernatant actively oxidizing uroporphyrinogen inhibited the oxidation and restored decarboxylation. The latter finding suggested that a labile inhibitor was formed during the oxidation. These results suggest uroporphyrinogen oxidation may be important in the mechanism of chemically induced uroporphyria.

The 1986 Upjohn Award Lecture. Interaction of chemicals with hemoproteins: implications for the mechanism of action of porphyrinogenic drugs and nitroglycerin

1987 ◽  
Vol 65 (6) ◽  
pp. 1111-1119 ◽  
Author(s):  
Gerald S. Marks
Keyword(s):  
Chick Embryo ◽  
Guanylate Cyclase ◽  
Inhibitory Activity ◽  
Liver Cells ◽  
Enzymatic Reactions ◽  
Uroporphyrinogen Decarboxylase ◽  
Nitrite Ion ◽  
Catalytic Activation ◽  
Embryo Liver ◽  
Cytochrome P 450

The ferrochelatase inhibitory activity of a variety of analogues of 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC) was studied in chick embryo liver cells. The ferrochelatase inhibitory activity of the 4-butyl, 4-pentyl, and 4-hexyl analogues was considered to be due to catalytic activation by cytochrome P-450 leading to heme alkylation and formation of the corresponding N-alkylporphyrins. The relative ferrochelatase inhibitory activity of the DDC analogues has implications for a postulated model of the binding of porphyrins in the ferrochelatase active site. 3-[2-(2,4,6-Trimethylphenyl)thioethyl]-4-methylsydnone (TTMS) was shown to be a potent porphyrinogenic agent and to inhibit ferrochelatase in chick embryo liver cells. A related sydnone, 3-benzyl-4-phenylsydnone did not inhibit ferrochelatase activity. These results supported the idea that the porphyrinogenicity of TTMS was due to catalytic activation by cytochrome P-450 leading to heme alkylation and formation of N-vinylprotoporphyrin which inhibits ferrochelatase. Polychlorinated biphenyls, phenobarbital, nifedipine, and a large number of structurally different chemicals which are porphyrinogenic in chick embryo liver cells inhibit uroporphyrinogen decarboxylase by an unknown mechanism. Thus drug-induced porphyrin biosynthesis in chick embryo liver cell culture appears to be caused by inhibition of either ferrochelatase or uroporphyrinogen decarboxylase. The biotransformation of nitroglycerin by human red blood cells is due to a combination of a sulfhydryl-dependent enzymatic process and an interaction with reduced hemoglobin. Biotransformation of nitroglycerin was shown to occur only with the deoxy form of hemoglobin and to involve a two-electron denization, resulting in the oxidation of two molecules of heme iron (II) per mole of nitroglycerin biotransformed to glyceryl dinitrate and nitrite anion. Since nitroglycerin biotransformation appears to be involved in the mechanism of nitroglycerin-induced vasodilation, we have suggested the following hypothesis: biotransformation of nitroglycerin in vascular smooth muscle might occur by interaction of nitroglycerin with the iron (ferrous) of guanylate cyclase-bound heme. The nitrite ion formed may be converted via nitrous acid to nitric oxide. This in turn would combine with the heme moiety of guanylate cyclase to activate the enzyme and through a series of enzymatic reactions cause vasodilation.

scholarly journals Induction of 5-aminolaevulinate synthase by two- to five-carbon alcohols in cultured chick-embryo hepatocytes. Relationship to induction of cytochrome P-450

1986 ◽  
Vol 234 (2) ◽  
pp. 405-411 ◽  
Author(s):  
J F Sinclair ◽  
L M Zaitlin ◽  
E L Smith ◽  
S K Howell ◽  
H L Bonkovsky ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Isopropyl Alcohol ◽  
Primary Cultures ◽  
Fold Increase ◽  
Common Mechanism ◽  
Uroporphyrinogen Decarboxylase ◽  
Synergistic Induction ◽  
Ethanol Ethanol ◽  
Dose Responses ◽  
Cytochrome P 450

The induction of 5-aminolaevulinate synthase and of cytochrome P-450 by short-chain aliphatic alcohols was compared in primary cultures of chicken-embryo hepatocytes. Isopropyl alcohol, isobutanol, pentan-1-ol and isopentanol alone caused up to a 4-fold increase in 5-aminolaevulinate synthase, whereas ethanol and propan-1-ol did not. Induction of the synthase by isopentanol was maximal at 8 h, and reached a plateau thereafter, whereas the activity induced by 2-propyl-2-isopropylacetamide continued to increase for 20 h. In the presence of 3,4,3′,4′-tetrachlorobiphenyl, an inhibitor of haem synthesis at the uroporphyrinogen decarboxylase step, synergistic induction of 5-aminolaevulinate synthase was observed with all the alcohols except ethanol. Ethanol, but not isopentanol, decreased the extent of induction of 5-aminolaevulinate synthase by 2-propyl-2-isopropylacetamide and 3,4,3′,4′-tetrachlorobiphenyl (50% decrease at 112 mM-ethanol). Total protein synthesis was not inhibited by ethanol in these cells. The composition of porphyrins was determined after treatment of cells with ethanol, isopentanol or 2-propyl-2-isopropylacetamide. Untreated cells, when incubated with 5-aminolaevulinate for 6 h, accumulated mainly protoporphyrin. However, when cells were pretreated with ethanol, isopentanol or 2-propyl-2-isopropylacetamide for 20 h, and 5-aminolaevulinate was added, 8- and 7-carboxyporphyrins increased, whereas protoporphyrin decreased. The dose responses for induction of either 5-aminolaevulinate synthase or cytochrome P-450 after a 20 h exposure to 3- to 5-carbon alcohols were identical. The results indicate that: simple alcohols can induce both enzymes; hydrophobicity increases their effectiveness; and induction of both enzymes are probably mediated by a common mechanism.

scholarly journals THE INFLUENCE OF POSTNATAL DEVELOPMENT ON DRUG-INDUCED HEPATIC PORPHYRIA AND THE SYNTHESIS OF CYTOCHROME P-450

1971 ◽  
Vol 134 (5) ◽  
pp. 1349-1371 ◽  
Author(s):  
Chull S. Song ◽  
Harold L. Moses ◽  
Alan S. Rosenthal ◽  
Nancy A. Gelb ◽  
Attallah Kappas
Keyword(s):  
De Novo ◽  
Perinatal Period ◽  
Regulatory Control ◽  
Laboratory Animals ◽  
Ultrastructural Changes ◽  
Drug Induced ◽  
Chemical Inducers ◽  
Mixed Function Oxidase System ◽  
Induced Changes ◽  
Cytochrome P 450

The mitochondrial enzyme δ-aminolevulinate synthetase (ALAS) controls the rate-limiting step in the synthesis of porphyrins and heme. An experimental form of hepatic porphyria can be readily elicited in laboratory animals, such as the rat, by drugs and foreign chemicals which are known to enhance the de novo formation of this enzyme in the liver. The present study shows that there is a striking refractoriness to the induction of ALAS during the perinatal period in the rat. Chemicals which have potent porphyria-inducing activity in adult animals have no significant inducing effect on hepatic ALAS in neonates. The ultrastructural changes which accompany the induction of ALAS by drugs and chemicals in adult liver also fail to take place in the livers of neonates. A progressive capacity for responding to the action of chemical inducers of hepatic ALAS does, however, develop in neonatal animals so that by approximately 5–6 wk of age experimental porphyria can be elicited as effectively in them as in adults. The reasons for the refractoriness of hepatic ALAS to induction in the perinatal period are not known; but the findings of this study make it clear that ALAS belongs to that increasingly large group of liver enzymes in mammals whose appearance, increase of activity, or inducibility is developmentally determined. The occurrence of developmental changes in the indicibility of ALAS in the liver of neonates also provided an opportunity to study the relationship of this enzyme activity to the drug-mediated induction of the hepatic hemoprotein cytochrome P-450. This inducible hemoprotein serves as the terminal oxygenase in the microsomal mixed-function oxidase system in the liver. The results of this study indicate that, in contrast to the refractoriness of ALAS to induction, significant drug-induced changes of hepatic P-450 content and of hemeprecursor incorporation into this cytochrome do take place in neonates. The synthesis of P-450 thus appears to be under a regulatory control different from that of ALAS in neonates, and the relation between ALAS activity and P-450 formation is not therefore a direct one.

Drug-Induced Porphyrin Biosynthesis—XII. Levels of Cytochrome P-450 in Chick Embryo Liver following Administration of Allylisopropylacetamide and Propylisopropylacetamide

1974 ◽  
Vol 52 (4) ◽  
pp. 891-895 ◽  
Author(s):  
V. Krupa ◽  
J. C. Creighton ◽  
M. Freeman ◽  
G. S. Marks
Keyword(s):  
Chick Embryo ◽  
Aminolevulinic Acid ◽  
The Other ◽  
Synthetase Activity ◽  
Drug Induced ◽  
Liver Cytochrome ◽  
Time Period ◽  
Embryo Liver ◽  
Ala Synthetase ◽  
Cytochrome P 450

Allylisopropylacetamide caused a decrease in the level of chick embryo liver cytochrome P-450 1 h after administration, followed by an elevation above control levels at a later time period. Propylisopropylacetamide on the other hand did not produce an early decrease in cytochrome P-450 but produced an elevation of cytochrome P-450 at a later time period. Since propylisopropylacetamide is an inducer of δ-aminolevulinic acid synthetase activity and porphyrin accumulation in chick embryo liver, it was concluded that a loss of cytochrome P-450 is not a prerequisite for ALA-synthetase induction as is thought to be the case in rats.

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